Characterization of the CO2 sources associated with the Bongwana fault: its impact on surface water and groundwater quality and implications for carbon capture and storage (CCS) in South Africa. Analysis and modeling of the impact of CO2 sources associated with Bongwana fault on fresh groundwater and surface water quality and implications for carbon capture and storage (ccs) in South Africa.
CHAPTER ONE: INTRODUCTION
H YPOTHESIS
R ESEARCH QUESTIONS
R ESEARCH AIM AND OBJECTIVES
Chapter Two: This chapter presents the geographical location of the study area and discusses the climatic, geological and hydrogeological conditions of the study area. Chapter Six: Discusses the findings of the study and presents the interpretation based on the results obtained.
CHAPTER 2: DESCRIPTION OF THE STUDY AREA
- L OCATION OF THE STUDY AREA
- C LIMATE AND DRAINAGE
- G EOLOGICAL SETTING
- H YDROGEOLOGICAL CONDITIONS
- Aquifer types
- General groundwater quality
The diamictites of the Dwyka Group are highly compacted and generally consist of angular to rounded clasts of the basement rocks embedded in a clay and silt matrix. The sandstones are generally very fine to medium grained, massive to ripple laminated, or medium to coarse grained, trough cross-bedded and immature (Von Brunn, 1994). Underlying the Dwyka Group rocks within the study area are the rocks of the Msikaba Formation.
CHAPTER 3: LITERATURE REVIEW
C ARBON DIOXIDE EMISSIONS AND CLIMATE CHANGE
- S OURCE OF CO 2
- Migration of CO 2 in the earth’s crust
- Impacts of dissolved CO 2 on water chemistry
- Technique to curb CO 2 release: Carbon Capture and Storage (CCS)
Most of the CO2 originating from magma degassing is released via volcanoes and associated fissures or hydrothermal vents such as Yellowstone National Park in the USA (BGS, 2005). Studies of the impacts of CO2 from CO2 sequestration sites reveal that the dissolution of CO2 in groundwater to form carbonic acid and its subsequent decomposition causes a decrease in pH.
Transportation
In the post-combustion method, CO2 is separated from the power plant flue gas by bubbling the gas through an absorber column packed with liquid solvents (such as ammonia) that preferentially remove CO2. In the most commonly used techniques, once the chemicals in the absorber column have become saturated, a stream of superheated steam at about 120°C is passed through it. Oxyfuel combustion systems use oxygen instead of air to burn the primary fuel to produce a flue gas that is mainly water vapor and CO2.
Further flue gas treatment may be required to remove air pollutants and non-condensable gases (such as nitrogen) from the flue gas prior to CO2. As a method of capturing CO2 in boilers, oxygen combustion systems are in the demonstration phase (see Table TS.1). Oxygen fuel systems are also being studied in gas turbine systems, but conceptual designs for such applications are still in the research phase (IPCC, 2005).
Storage
P REVIOUS STUDIES ON THE B ONGWANA FAULT
Natural CO2 sources at the Bongwana area were first studied in the early 20th century by Young (1923) and Gevers (1941). Further work carried out by Gevers (1941) and Du Toit (1946) led to the identification and characterization of the other CO2 sources associated with the deposition of the travertine cones near Umtamvuna River, south of the Bongwana area. These CO2 sources are believed to be associated with an 80 km long N-S trending fault known as Bongwana Fault (Harris, et al., 1997).
Young (1923) postulated that CO2 gas arises from faults in the Dwyka tilites, indicated on the surface by silicified wall rock. The carbon and isotope data published by Harris et al., (1997) for CO2 gas from the Bongwana fault indicated a carbonate source for CO2 production in favor of the Gevers model. However, there is no isotope data to support this. The assumption was based on the fact that the two groundwater sources exhibit the same temperatures.
CHAPTER 4: RESEARCH METHODOLOGY
D ATA COLLECTION
- Desktop study
- Literature review
- Data consolidation
The literature review used all available information from previous studies into the effects of CO2 on groundwater and surface water supplies. The literature review included, but was not limited to, examining papers, articles and books on the origin of CO2 from natural and anthropogenic processes, the storage of carbon dioxide in deep geological formations and related water quality issues associated with CO2 leakage from the storage location. . Harries (1997) on the Bongwana fault and associated CO2 emissions were obtained and used as a basis for the desktop assessment.
In addition to the above, available methods to capture and transport CO2 from the source area to a storage facility and the suitability of the geological formation for storing CO2 were also studied. All the data collected from the desk study and literature review were merged and the site maps were compiled for the field assessment phase. The literature review results were used to decide the hydrochemical determinants to be analyzed from the samples collected in the field that would indicate the impact of CO2.
F IELD ASSESSMENT
- Preliminary field assessment
- Hydro-census and sample collection
- Field measurements
Preliminary field water quality parameters were measured at the CO2 sites and used to design a detailed hydrocensus and field sampling protocol for subsequent hydrochemical analyses. Following the results of the preliminary site assessment, a detailed hydrocensus of approximately 10 km was carried out on both sides of the Bongwana Fault. Samples were filtered on site and stored in coolers before being transported to the laboratory for hydrochemical analysis.
A volume of 100 ml of the collected sample was used to titrate the sample using hydrochloric acid and phenolphthalein indicator to pH 4.5 to determine the total alkalinity of the sample. The total volume of hydrochloric acid used to reach the pH endpoint was recorded and used to calculate the total alkalinity and bicarbonate concentration using the following formula proposed by Snoeyink and Jenkins (1980). Two travertine rock samples were crushed to a fine powder at the UKZN Geological Sciences Laboratory and analyzed by XRD and XRF.
D ATA ANALYSIS , INTERPRETATION AND CONCEPTUALIZATION
Samples were analyzed using ELAN 6100 inductively coupled plasma mass spectrometer (ICP-MS) for trace element analysis and an ion chromatograph (IC) for major ion analysis. Thin sections were made from travertine rock samples collected from the Umtamvuna River and analyzed under a polarized microscope.
CHAPTER 5: RESULTS
F IELD MEASUREMENTS
The site is identified by carbon dioxide gas bubbles from the riverbed emerging from an approximately 20m wide fault pit. Borehole located within the Big Bend farm, north of the Bongwana train station, about 300m from the turn off on the N2 road to Umzimkulwana River through the dirt road.
W ATER QUALITY AND HYDROCHEMISTRY
BGN-1 Reka Umzimkulwana Površinska voda Na-Mg-Ca-HCO3-Cl Da BGN-11 Reka Umtamvuna Podzemna voda Na-Ca-Mg-HCO3 Da BGN-12 Reka Umtamvuna Podzemna voda Na-Ca-Mg-HCO3 Da BGN-14 Reka Umtamvuna Površinska voda Na-Mg-Ca-HCO3-Cl No BGN-15 Reka Umtamvuna Podzemna voda Na-Ca-Mg-HCO3 Da BGN-16 Reka Umtamvuna Podzemna voda Na-Ca-Mg-HCO3 Da.
Linkages among geochemical parameters of groundwater
Poor correlation between the concentration of Mg2+ and HCO3 in the boreholes suggests that it is unlikely that the dolomite solution is responsible for the observed concentration of Mg2+ and HCO3. However, good correlations between the concentration of Ca2+ and HCO3- and between Na+ and Cl- are observed.
Saturation indexes of groundwater and surface water with respect to selected minerals
This suggests that water from travertine cone springs is supersaturated with respect to these carbonate minerals. However, the SIs of Anhydrite and gypsum for travertine cone sources appear to be negative, implying that these minerals are expected to dissolve or be absent in the groundwater flow path. Shallow groundwater from the boreholes within the study area appears to be undersaturated (negative SIs) with respect to calcite, dolomite, anhydrite, gypsum and aragonite.
G EOCHEMICAL COMPOSITION OF TRAVERTINE ROCK SAMPLES
H YDROGEOCHEMICAL INVERSE MODELING
H YDROGEOCHEMICAL FORWARD MODELING
The lines show the steps of the forward model and the dots at the end of the lines show the average concentration measured from the travertine sources.
E NVIRONMENTAL ISOTOPE SIGNATURES
CHAPTER 6: DISCUSSION
- CO 2 IMPACTS ON GROUNDWATER AND SURFACE WATER
- E VOLUTION OF GROUNDWATER HYDROCHEMISTRY
- O RIGIN OF CO 2
- O RIGIN AND AGE OF GROUNDWATER
- I MPLICATION FOR CCS IN S OUTH A FRICA AND THE NEED FOR ROBUST MONITORING
- L ESSONS LEARNT FROM THE B ONGWANA STUDY
- S HALLOW GROUNDWATER MONITORING SYSTEM
- H YDROGEOLOGICAL CONCEPTUALIZATION OF THE OCCURRENCE AND CIRCULATION OF SHALLOW GROUNDWATER
The supersaturation of the groundwater from these sources with carbonates is also shown by the deposition of the travertine mounds. Assuming that the carbonate rocks exist at depth below the study area, the water percolating through the overlying pyritic carbonaceous shales of the Ecca Group and Dwyka Group sediments leaches pyrite from these sediments. The difference is also clearly seen in the stable isotope composition of the water samples.
This research presents the groundwater parameters indicative of CO2 interaction with freshwater resources based on the analysis of the Bongwana monitoring project. The results of the field measurements and hydrochemical information obtained from the Bongwana study show clear effects of natural CO2 on groundwater and surface water quality. In addition to the field measurements, the analysis of the changes in the surrounding groundwater quality near the binding site is also important.
CHAPTER 7: CONCLUSIONS AND RECOMMENDATIONS
C ONCLUSIONS
Additionally, inverse geochemical modeling results for travertine cone springs indicate that the mineral phases contributing to the overall spring chemistry are primarily carbonate minerals. Although the Dwyka Group sediments contain some carbonate minerals that may affect groundwater chemistry, it is possible that carbonate rocks at depth account for the volume of carbonate minerals dissolved in groundwater and the formation of travertine mounds at the surface. The Bongwana fault and associated CO2 sources present an excellent analog for understanding the impacts of CO2 leakage due to injection well failure or leakage from an abandoned well or gradual leakage through undetected faults, fractures or wells from a site. failed CO2 storage.
The findings of this study provide a clear picture of the impacts of CO2 on groundwater and surface water resources. It is worth noting that South Africa is currently experiencing water shortages due to prolonged drought conditions in most parts of the country. However, it is believed that rigorous scientific site selection protocols and CO2 leak detection monitoring systems, along with appropriate on-site remedial plans, are most likely to minimize the risk of CO2 leakage from an underground sequestration facility.
R ECOMMENDATIONS
The tectonic, metamorphic and intrusive history of the Natal Mobile Belt between Glenmore and Port Edward. Karolyte, R., Sascha Serno, S., Johnson, G and Gilfillan, S.M.V. The influence of oxygen isotope exchange between CO2 and H2O in natural CO2-rich spring water: implications for geothermometry. Petrolology, origin and metamorphic history of Proterozoic granulites from the Natal Metamorphic Province, Southeast Africa.
A Graphical Procedure in the Geochemical Interpretation of Water Analysis, United States Department of the Interior, Geological Survey, Water Resources Division, Groundwater Branch, Washington, 63pp. 1992) Geochemical Modeling of Water-Rock Interaction: Past, Present, Future", in Water-Rock Interation, Vol. Glaciogenic Deposits of the Permo-Carboniferous Dwyka Group in the Eastern Region of the Karoo Basin, South Africa, in Deynoux, M ., Miller, J.M.G., Domack, E.W., Eyles, N., Fairchild, I.J., and Young, G.M., eds., Earth's Glacial Record: Cambridge, Cambridge University Press, 60-69. A hydrochemical framework and water quality assessment of rivers water in the upper reaches of the Huai River basin, China, Environ.
CHAPTER 8: REFERENCES
